[Ion channel diseases in neurology].

Since 1990, many mutations, in genes encoding ion channels have been discovered to cause disorders characterized by hyper- or hypoexcitability of skeletal muscle or the central nervous system (CNS): i) mutations in the muscle chloride channel gene lead to a loss or change of function of the channels and cause an abnormally low total chloride conductance resulting in hyperexcitability of the muscle fiber membrane in the dominant and recessive form of myotonia congenita; ii) numerous dominant point mutations in the gene encoding the muscle sodium channel alpha-subunit cause incomplete sodium channel inactivation. Dependent on the inactivation parameter altered and the degree of the gain of function induced by a given mutation, the muscle episodically becomes hyper- or hypoexcitable (i.e. stiff or weak), particularly in response to elevated serum potassium (potassium-aggravated myotonia, hyperkalemic periodic paralysis) or cold environment (paramyotonia congenita); iii) dominant point mutations in the gene coding for the muscle L-type calcium channel alpha(1)-subunit can cause episodes of muscle inexcitability (i.e. weakness), particularly in response to lowered serum potassium (hypokalemic periodic paralysis); despite the recently discovered etiology of the disease, the pathogenesis of the weakness is still unknown; iv) dominant mutations in a voltage-gated potassium channel expressed in the CNS cause episodic ataxia type 1 presumably by antagonizing repolarization of the cell membrane; v) dominant mutations in a neuronal calcium channel alpha-subunit may cause either episodic ataxia type II or familial hemiplegic migraine by a so far unknown pathomechanism; vi) the first mutation in an ion channel associated with an inherited form of epilepsy, nocturnal frontal lobe epilepsy, was found in the alpha(4)-subunit of a neuronal nicotinic acetylcholine receptor.